Feed Screw For Eccentric Screw Pump

ABSTRACT

The inventions relates to a feed screw for eccentric screw pumps which, to avoid bridge formation of the medium and optimisation of the drive power, has a screw, which in the axial region, has perforations and webs.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of German patent application No. 10 2006 036 243.8 filed on Aug. 3, 2006, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to an eccentric screw pump with a feed screw which supplies the suction region of the screw rotor mainly with medium to highly viscous media.

BACKGROUND OF THE INVENTION

DE 101 60 335 A1 shows an eccentric screw pump in this regard where a feed screw is arranged in the pump housing before the pump rotor. The screw is connected with the screw core via its entire inner contour.

DE 101 18 071 A1 shows an eccentric screw pump about the coupling rod of which a hollow screw is arranged. This hollow screw is connected with a disc on the drive side. The other end in the suction-side region of the screw rotor has no connection to a joint or the coupling rod.

With a mixing device according to DE 1 277 819 dry substances are mixed with liquid and subsequently delivered by a pump. To this end, a mixing screw is seated in the region of a storage vessel, which mixing screw is connected on the one side with a motor and, on the other side with a screw pump. Liquid enters the screw region between the storage vessel and the pump. The feed screw consists of a helical band which is only fastened to the mixer shaft at one end by means of four braces.

A mixing and feed device is also shown in DE 43 18 177. The dry substances enter the region of a mixing screw via a hopper, while a liquid feed line also leads into the region of said mixing screw. Following the mixing operation, the mixture is transported onwards by a screw pump. The mixing screw itself consists of a region with a solid screw and a region with paddle and web-shaped mixing elements.

Each pump is designed for a determined delivery rate. To this end, adequate medium must always be available for the pump region on the suction side. The feed screws, which are arranged upstream of the actual screw or eccentric screw pump, can therefore deliver a multiple volume of the pump capacity. Because of this, a back-up effect develops in the so-called stuffing space in the suction region which is associated with danger of bridge formation in the hopper above the screw. Because of this stuffing effect, substantially higher drive power than necessary must be made available.

The object of the invention consists in adapting the stability of the feed screw to the required output while keeping the drive power constantly low even with different media.

SUMMARY OF THE INVENTION

This object is solved through the characteristics of claim 1. Further developments of the feed screw according to the invention are indicated from the characteristics of the sub-claims.

The design of a corresponding feed screw between the pump rotor and the drive has shown that the devices known from the prior art solve only part problems of the object according to the invention.

The design according to the invention is obviously dependent on which products with which viscosities, and, if applicable, present solid materials have to be pumped.

According to the invention the normal embodiment concerns a feed screw having at least two perforations, wherein the webs formed between these perforations are connected with their screw root with the coupling shaft. Depending on which viscosity the product has it may be practical to increase the number of perforations to at least four in order to facilitate the return flow of the medium and ensure more homogenous mixing-through, through which bridge formation of the medium is already counteracted on the suction-side end of the pump.

Through the perforations according to the invention, low-loss drive power compared with delivery devices from the prior art, designed to the condition of the medium can be installed.

In order to obtain the advantage according to the invention also in the regions of the couplings (joints) the screw also extends beyond this region for the purpose of which the pipe employed as coupling rod has strip-shaped pipe segments which are connected with the screw. If the number of the pipe segments corresponds to the number of the perforations, a corresponding number of webs for their fastening is available.

Since for the return flow of the medium not only the number of perforations but also their area place a substantial role, it can be provided according to a version according to the invention to dimension the perforations between 30% and 70% of the height of the screw start. With low-viscosity substances the height of the perforations can be selected in the range from 20% to 60% of the height of a screw pitch.

As is shown in an exemplary embodiment the width of the perforations will correspond to the width of the webs because of the homogenous return feed and even loading of the screw. With high-viscosity media the return flow possibility must certainly be improved wherein the width of the perforations is greater than the width of the webs. With low viscosity substances the danger of bridge formation is relatively low so that here the width of the webs can be greater than that of the perforations.

To improve the return flow and thus reduce the stagnation effect the flow along the coupling shaft can be improved in that the webs have an inclination and thus produce a flow direction which is opposite to the course of the screw.

Depending on which design of the screw is required, the webs can be offset to one another by 30° to 120° per screw start. In order for the feed screw to be stabilised about its entire length through the coupling shaft the length of the pipe segments is adapted to the course of the feed screw.

Easier affixing of the feed screw to the coupling shaft is obtained in that the feed screw consists of several parts which enable better handling during the mostly employed welding operation.

The invention is exemplarily described in the following by means of exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 lateral view of the feed screw;

FIG. 2 a three-dimensional representation of the feed screw;

FIG. 3 a cross section of the feed screw;

FIG. 4 feed screw with joint part on both sides;

FIG. 5 lateral view of the feed screw according to FIG. 4;

FIG. 6 cross section of a feed screw;

FIG. 7 screw cross section with 6 perforations;

FIG. 8 screw cross section with 4 perforations; and

FIG. 9 screw cross section with various perforation distances from the coupling rod.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a design possibility of a feed screw 10 with a screw pipe 12. A screw 14 is welded on to the circumferential surface of the screw pipe 12. On both ends 16, 18 of the screw pipe 12, pipe segments 20 for fastening the screw 14 are provided. Each of the pipe segments 20 ends at the point at which the screw 14 ends in axial direction. In the region of the pipe elements 20, couplings 22 for the joints not shown are provided at both ends. The screw 14 is manufactured from flat band-shaped material.

The design of the screw 14 can be more clearly seen in FIG. 2. From the perspective representation it becomes evident that the screw 14 is provided with perforations 24 and webs 26. Each screw root 34 of the webs 26 is connected with the pipe segment 20 or the coupling shaft 32 for example through a welding operation. While the medium in axial direction flows from the rotor region back to the pump inlet through the perforations of the feed screw closely along the screw pipe, the screw 14 with its end faces 28 transports the medium in the direction towards the pump rotor. The pump rotor, through a joint which is not completely shown, and which joint is fastened to the coupling 22, is in positive contact with the feed screw.

FIG. 3 shows the embodiment and arrangement of the perforations 24 and webs 26 for a feed screw for highly viscous media. Here, the large free areas of the perforations 24 enable very good return flow possibilities for the medium in order to adapt the stagnation pressure in the stuffing space to the pump output. Here, dehydration of the medium and increased tendency toward bridge formation is prevented and undesirably high drive power avoided.

The perforations 24 according to this exemplary embodiment are wider than the webs 26. The middle of the perforations in each case is located on the midperpendicular and is thus offset by 90° relative to one another which produces 4 perforations 24 and 4 webs 26 per screw pitch. The height of the perforations corresponds to approximately 50% of the screw height.

A feed screw 10 is also shown in FIG. 4 and FIG. 5. Here, a coupling shaft 32 is provided as drive component. A screw 14 is welded on to the coupling shaft 32 in the region between the joint components 30 which, as with all other exemplary embodiments, consists of individual screw segments. This embodiment of the screw 14 is employed for instance with low-viscosity media. By way of the large face areas 28 compared with the areas of the perforations 24, more medium enters the rotor region while the smaller dimensioned perforations nevertheless prevent an increased need for drive power.

The arrangement of the perforations 24 and their size of the feed screw 10 shown in FIGS. 4 and 5 is shown in FIG. 6. Per screw pitch, three perforations each offset by 120° are provided in the screw 14.

Additional exemplary embodiments for the screw design for one winding each are shown in FIGS. 7, 8, 9.

FIG. 7 represents an even distribution of 6 perforations 24 and webs 26. The height HD of the perforations is 50% compared with the height HS of the screw 14. The width BD of the perforations corresponds to the width BS of the webs.

In FIG. 8 the screw 14 has four perforations 24 and four webs 26 while the width BD of the perforations is greater than the width BS of the webs. The height HD of the perforations 24 is 50% of the height HS of the screw 14.

The interrupted lines of FIG. 9 shows different size relationships with regard to the height HD of the perforations to the height HD of the screw 14, while three perforations 24 are shown with a division by 120. 

1. An eccentric screw pump with an eccentrically rotating rotor which rotates in a stator provided with an additional screw start, wherein the rotor is connected with a drive via a coupling shaft and the coupling shaft is surrounded by a feed screw, characterized in that the feed screw has a screw which, per pitch, has at least two perforations and that the webs formed between these perforations are connected with the coupling shaft.
 2. The eccentric screw pump according to claim 1, characterized in that at least four perforations are present per screw pitch.
 3. The eccentric screw pump according to claim 1, characterized in that the coupling shaft has a screw pipe on which strip-shaped pipe segments are located at one end parallel to the longitudinal axis of the feed screw which are connected with the screw.
 4. The eccentric screw pump according to claim 3, characterized in that the number of pipe segments corresponds to the number of perforations.
 5. The eccentric screw pump according to claim 1, characterized in that the height of the perforations corresponds to between 30% and 70% of the height of the screw.
 6. The eccentric screw pump according to claim 5, characterized in that the height of the perforations corresponds to between 20% to 60% of the height of the screw.
 7. The eccentric screw pump according to claim 3, characterized in that the pipe segments in the operational state cover the joint element/s.
 8. The eccentric screw pump according to claim 1, characterized in that the width of the perforations corresponds to the width of the webs which are connected with the coupling rod.
 9. The eccentric screw pump according to claim 1, characterized in that the width of the perforations is greater than the width of the webs.
 10. The eccentric screw pump according to claim 1, characterized in that the width of the webs is greater than the width of the perforations.
 11. The eccentric screw pump according to claim 1, characterized in that the webs have an inclination opposite to the course of the screw.
 12. The eccentric screw pump according to claim 1, characterized in that the webs are offset to one another by 30° to 120°.
 13. The eccentric screw pump according to claims 7, characterized in that the length of the pipe segments is adapted to the course of the screw.
 14. The eccentric screw pump according to claim 1, characterized in that the screw consists of several parts.
 15. The eccentric screw pump according to claim 2, characterized in that the coupling shaft has a screw pipe on which strip-shaped pipe segments are located at one end parallel to the longitudinal axis of the feed screw which are connected with the screw.
 16. The eccentric screw pump according to claim 2, characterized in that the height of the perforations corresponds to between 30% and 70% of the height of the screw.
 17. The eccentric screw pump according to claim 4, characterized in that the height of the perforations corresponds to between 30% and 70% of the height of the screw.
 18. The eccentric screw pump according to claim 4, characterized in that the pipe segments in the operational state cover the joint element/s. 